Added fancy "tree" command to the sample runner that dumps the structure of a DirectoryLayer juste like the Unix "tree" command.
Added a few XML comments
Fixed invalid conversion of Slices to string and booleans

- Slice => string was decoded as ASCII instead of Unicode
- Slice => bool considered the byte array { 0 } to be true
- added Slice.ToBool(), Slice.FromUInt32() and Slice.FromFixedU32() methods
Refactored the ISliceSerializable interface, added ISliceSerializer<T> [Work in Progress]

- Allows custom classes to be serialized to Slices (and back), which should simplify Layers that just want to quickly pack/unpack values
- FdbSliceSerializer<T>.Default will attempt to create the best serializer from the T (using Tuples or Converters when possible, also recognizes classes that implement ISliceSerializable)